One bipolar modulation technique for the transmission of digital information is known as Alternate Mark Inversion (AMI) in which positive pulses known as P DATA are separated from negative pulses known as N DATA by a zero reference. What is called R DATA is the OR'd combination of P DATA and N DATA. This serial format is usually divided into frames by the use of an intentional code violation in which two successive logical "ones" have the same polarity e.g., two successive P DATA pulses or two successive N DATA pulses. Such a format does not lend itself to direct application to digital equipment. Further difficulties are encountered because the amplitude of the pulses may vary by a ratio of as much as 50:1.